Inotrope
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An inotrope is an agent which increases or decreases the force or energy of muscular contractions. Negatively inotropic (in·o·trop·ic) (in²o-trop¢ik) [ino- + -tropic] agents weaken the force of muscular contraction. Positively inotropic agents increase the strength of muscular contraction.
The term is often used in reference to the way various drugs affect the strength of contraction of heart muscle (myocardial contractility).
Inotropic drugs
Drugs available are generally cathecholamines (increasing intracellular cAMP via adenylate cyclase stimulation; increasing intracellular calcium and thus cardiac force of contraction) which include: adrenaline, noradrenaline, isoprenaline, dopamine, dobutamine, dopexamine(synthetic dopamine-like drug, more specific for dopamine receptors), phosphodiesterase inhibitors (eg. enoximone, caffeine), calcium sensitisers (levosimendan) and other related agents (calcium, digoxin, glucagon).
The choice of drug depends on the clinical circumstance and may be used singly or in combination with vasodilator drugs: dopamine (previously thought have a renal protective effect at low doses, but subsequently debunked by studies. Remains controversial though.), dobutamine (cardiac support), adrenaline (inotropic and vasoconstriction) and enoximone (post cardiac surgery where tachycardia is undesirable).
Each inotrope has different effects on groups of receptors - alpha 1 and 2, beta 1 and 2, dopamine receptors, and subdivisions of these. The different receptors are present in different tissues hence the different relative effects of each different inotrope. The drug of choice in any given clinical scenario is often contoversial and in practice, many situations will benefit from any inotrope and the argument is moot. Often the first line choice is based on sound theory - for example, adrenaline is used to treat septic shock (where the blood pressure cannot be maintained due to massive dilatation of the blood vessels) because its effects include, firstly, an inotropic effect on heart contractility (through beta 1 stimulation) and secondly, constriction of the blood vessels (alpha 2 stimulation) to reverse the fundamental problem.